Filter wheel

ABSTRACT

An improved filter wheel is disclosed, through embodiments, that comprises a plurality of reflector support structures formed as a unitized structure with a circular base member. In some embodiments, the filter wheel further comprises a plurality of light sources mounted on the filter wheel.

CROSS-REFERENCE TO RELATED APPLICATION

This Utility Patent Application is a continuation application of patentapplication Ser. No. 13/847,393, filed Mar. 19, 2013, (allowed), whichis a continuation application of patent application Ser. No. 13/009,331,filed Jan. 19, 2011, (now U.S. Pat. No. 8,398,263), which claimspriority of U.S. Provisional Patent Application No. 61/296,543, filedJan. 20, 2010, which is incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION

An epifluorescence microscope is similar to a conventional reflectingoptical microscope in that both microscopes illuminate the sample andproduce a magnified image of the sample. An epifluorescence microscope,however, uses the emitted fluorescent light to form an image whereas aconventional reflecting optical microscope uses the scatteredillumination light to form an image. The epifluorescent microscope usesa higher intensity illumination, or excitation, light than aconventional microscope. The higher intensity excitation light is neededto excite a fluorescent molecule in the sample thereby causing thefluorescent molecule to emit fluorescent light. The excitation light hasa higher energy, or shorter wavelength, than the emitted light. Theepifluorescence microscope uses the emitted light to produce a magnifiedimage of the sample. The advantage of a epifluorescence microscope isthat the sample may be prepared such that the fluorescent molecules arepreferentially attached to the biological structures of interest therebyproducing an image of the biological structures of interest.

BRIEF SUMMARY OF INVENTION

In embodiments there is presented a filter wheel apparatus comprising: aplanar circular base member with a mechanical shaft coupler located atan axis of rotation defined perpendicular to and centered on thecircular base member, the circular base member penetrated by a pluralityof base apertures whose centers are angularly spaced about thecircumference of a circle, the centers of each of the base aperturesdefining an aperture axis perpendicular to plane of the aperture, theplanar circular base member further comprising a corresponding pluralityof reflector support structures, each of the reflector supportstructures being located in proximity to each of the plurality of baseapertures; a plurality of dichroic reflectors that transmit light at afirst band of wavelengths and reflect light at a second band ofwavelengths, each of the plurality of dichroic reflectors affixed to oneof the reflector support structures and thereby intercepting theaperture axis and oriented at approximately forty-five degrees anglerelative to the plane of the base aperture. While forty-five degrees ispreferred, other embodiments can use other angles.

In an embodiment, the filter wheel apparatus may further comprise: aright circular cylinder member surrounding and attached to the planarcircular base member thereby forming a cylindrical perpendicular wall; aplurality of wall apertures formed in the cylindrical perpendicular wallat angular locations corresponding to the plurality of base apertures,each of the wall apertures defining a wall aperture axis centered on andperpendicular to the wall aperture and intercepting a correspondingdichroic reflector.

In another embodiment, the filter wheel may further provide that eachthe reflector support structure comprises an individual excitation lightsource oriented to radiate toward the dichroic reflector. The individualexcitation light source may be at least one light emitting diode (LED)or laser.

BRIEF DESCRIPTION OF DRAWINGS

The present invention may be understood more fully by reference to thefollowing detailed description of the invention, illustrative examplesof specific embodiments of the invention and the appended figures ofembodiments in which:

FIG. 1 is a simplified schematic diagram of the optical path of anepifluorescene microscope.

FIG. 2 is a simplified schematic diagram of an embodiment of a filterwheel positioned in a microscope system.

FIG. 3 is a simplified schematic diagram of a top view of an embodimentof a filter wheel.

FIG. 4 is a simplified schematic diagram of a side view of an embodimentof a filter wheel.

FIG. 5 is a simplified schematic diagram of a bottom view of anembodiment of a filter wheel.

FIG. 6 is a simplified schematic diagram of a cutaway view of an portionof an embodiment of a filter wheel.

FIG. 7 is a simplified schematic diagram of a bottom view of anembodiment of a filter wheel comprising an individual excitation lightsource.

FIG. 8 is a simplified schematic diagram of a cutaway view of anembodiment of an optical component module having an individualexcitation light source.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a simplified schematic view of an epifluorescene microscope.An excitation filter 220 filters excitation light generated by a lightsource 210. The excitation filter 220 is preferably a band-pass filterallowing excitation light frequencies, falling within a first band ofwavelengths, matched to the fluorescent tags in the sample to passthrough while absorbing light of wavelengths outside the pass band. Theexcitation light is redirected by reflection from a dichroic mirror 230through an objective lens 240 to illuminate a sample 200 havingfluorescent tag molecules. The excitation light causes the fluorescenttag molecules to emit fluorescent light, at a second band ofwavelengths. The fluorescent light emitted by the tag molecules iscollected by the objective lens 240 and is transmitted through thedichroic mirror 230. The dichroic mirror 230 is selected to reflect theexcitation light at the first band of wavelengths, emitted by the lightsource 210 toward the sample 200, while transmitting the emission lightat the second band of wavelengths, emitted by the fluorescent tagmolecules contained in the sample through the dichroic mirror. Theemission light is then filtered by an emission filter 250 to removeextraneous light such as scattered excitation light. The emission lightis formed into an image by an imaging lens 260.

For applications requiring the imaging of multiple tag modules havingdifferent excitation/emission wavelength characteristics, multiple setsof filters and dichroic mirrors, each having properties tuned to one setof excitation/emission wavelengths are sequentially placed in theoptical path. Due to time constraints, the interchange of wavelengthspecific filters and dichroic reflectors must be quickly performed. Theminimization of overall test duration as well as minimization of theinterval between sequential exposures may be facilitated by employing afilter wheel comprising a plurality of optical component sets, each setbeing tuned for a specific excitation/emission light frequency pairing.

FIG. 2 is a simplified schematic view of a portion of a microscopesystem 360 comprising a filter wheel 10 that cyclically provides asequence of optical configurations. In this embodiment, the filter wheelintercepts the microscope optical axis between the objective lens andthe image portion of the microscope. Each optical configurationavailable on the filter wheel provides one of a predetermined set offiltering characteristics. An actuator 300 rotates the filter wheel 10thereby inserting the succession of optical component configurationsinto the microscope's optical axis 310. An excitation light source 320sequentially illuminates each set of optical component sets as the wheel10 rotates. The excitation light is reflected down to the specimen 330being examined. Light emitted from the specimen 330 propagates up themicroscopes optical axis 310 and is transmitted via the objective lenssystem 350, back through the filter wheel 10 and into the image portion355 of the microscope. Image portion 355 may comprise image formingoptical components for viewing and/or image capturing devices such ascameras or sensors. In alternate embodiments, the filter wheel 10 may belocated between the objective lens 350 and the specimen 330.

There are several filter wheel design approaches. The first approach,applicable to epi or reflected light illumination systems, uses a filtercube containing both the excitation and emission filters and acorresponding dichroic reflector. Multiple detachable filter cubes, eachtuned to the required wavelength combination, may be mounted on aturntable-like filter wheel. A single excitation light source, locatedexternal to the filter wheel, directs light into the filter cube when itrotates into view. The filter wheel rotates, sequentially exposingsuccessive filter cubes to the excitation light source and placing thefilters and reflector in the optical path. This approach, employingdetachable filter cubes, may suffer from:

-   -   1) difficulty in maintaining alignment of both the components        within the cube    -   2) cube to cube optical transmission characteristic variations        introduced by differences in individual optical component        properties.    -   3) excessive mass of the individual filter cubes and their        fixtures for mounting on the filter wheel that impact the speed        and control of the assembly    -   4) difficulty in maintaining alignment, for each of the filter        cubes, with the excitation light source.    -   5) sub-par light source performance due to need to generalize        performance across multiple wavelengths from one end of the        spectrum to the other.

An improved filter wheel 10 remedies many of the deficiencies ofdetachable cube designs. In an embodiment of the improved design, thecubes are eliminated and replaced by non-detachable optical componentmodules 15 that are an integral part of the filter wheel. Theintegration of the optical component modules 15 into the wheel itselfimproves mechanical precision and balance, reduces mass, and reducesparts count. The improved filter wheel 10 can be manufactured either bymolding out of a reinforced plastic, casting or machining out of alightweight metal such as aluminum, zinc or a suitable alloy. Thisconfiguration also provides the capability to increase the number offilter configurations within the assembly, for the same size envelope,as compared to other design approaches.

In an embodiment of the improved design, as shown in FIGS. 3 through 6,the filter wheel 10 is formed as a hollow right circular cylinder,comprising a cylindrical wall 20 attached at its top edge to a planarcircular solid base member 30. An axis of rotation 40 is definedperpendicular to and centered on the circular solid base member 30. Amechanical shaft coupler 45 is positioned where the axis of rotation 40penetrates the circular solid base member 30. The mechanical shaftcoupler 45 is configured to fixedly fasten the filter wheel 10 to ashaft that may be rotated by an actuator or motor 300. The rotationalposition of the filter wheel 10 may be determined and telemetered bysensors 12 located on, or in proximity to, the filter wheel 10. In anembodiment, the sensors 12 may be mounted directly to the shaft. Thecircular solid base member 30 is penetrated by a plurality of baseapertures 50 whose centers are spaced about the circumference of acircle having a radius less than that of the circular solid base member.While eight apertures are illustrated, any number of apertures may beemployed. Each of the base apertures 50 defines a first optical axis 60perpendicular to and centered on the corresponding base member aperture50. A first filter retaining structure 70 may be associated with each ofthe base apertures 50 and is configured to secure an optical filter 80across the respective base member aperture 50. In a non-limitingembodiment, optical filter 80 may be a band pass filter that transmitslight falling within a band of emission wavelengths while attenuatinglight having other wavelengths.

A plurality of dichroic reflector support structures 90, each associatedwith a corresponding base aperture 50, are integrated into the circularsolid base member 30. Each of the dichroic reflector support structures90 is configured to secure a separate dichroic reflector 100, centeredon the first optical axis 60, below and at a predetermined angle withrespect to the corresponding base member aperture 50. In a non-limitingembodiment, the predetermined angle is approximately forty-five degrees.The dichroic reflector 100 is selected to reflect light at theexcitation wavelengths while transmitting light at the emissionwavelengths. The dichroic reflector 100 is configured to change thedirection of propagation of the excitation light, from the first opticalaxis 60 to a second optical axis 110. The second optical axis 110 isparallel to a radial line segment 120 extending from the center of thecircular solid base member 30 to the center of the respective basemember aperture 50.

A plurality of wall apertures 130 penetrate the cylinder wall 20 atpoints corresponding to each of the second optical axis 110 interceptionpoints. A second filter retaining structure 140 may be associated witheach of the wall apertures 130 and configured to secure an opticalfilter 150 across the respective wall aperture 130. Optical filter 150transmits excitation light wavelengths while attenuating otherwavelengths.

In operation, the filter wheel 10 is employed as a component of anautomated microscope system. The filter wheel assembly may comprise aplurality of optical component modules 15 positioned at angularintervals around the filter wheel. Each of the optical modules 15further comprising the filters, dichroic reflectors, and apertures tunedfor each of the excitation/emission frequency combinations. In anembodiment, the optical component modules 15 are formed as an integralportion of the filter wheel assembly. The filter wheel 10 is configuredso that as it rotates about its axis of rotation 40, the first opticalaxis 60 of each of the successive base apertures sequentially comes intoco-axial alignment with the microscope's optical axis. An excitationlight source 160, external to the filter wheel, is configured to projectlight through wall aperture 130 toward the first optical axis 60. As thefilter wheel 10 rotates, successive wall apertures 130 sequentially comeinto alignment with the excitation light source 160 thereby admittingthe light into the interior of the cylinder. An optical filter 150, thatselectively transmits light of a first wavelength while rejecting lightat other wavelengths, may be located within the aperture 130. Theadmitted beam of light is filtered by optical filter 150 and thenredirected by reflection from the corresponding dichroic reflector 100,coaxially with the first optical axis 60 thereby illuminating thespecimen. The dichroic reflector 100 selectively reflects light of thefirst wavelength but transmits light at the second wavelength.

Portions of the specimen when exposed to excitation light at a firstwavelength fluoresce at a second light wavelength.

Light returning from the specimen, at the second wavelength, along thefirst optical axis 60 is transmitted through the dichroic reflector 100with a minimum reflection and propagates through the corresponding basemember aperture 50. An optical filter 80, selectively transmitting lightof the second wavelength, may be located within the aperture 50. Thelight exiting the base member aperture 50 propagates toward theobjective lens section of the microscope.

In another embodiment, the excitation light filter 150 may not berequired if the excitation light source 160 emits light having asufficiently narrow band spectrum. Specifically tuned LEDs (lightemitting diodes) or lasers may provide suitable narrow band light.Multiple narrow band light sources may be employed as required by theanalysis protocol.

In additional embodiments, the external excitation light source 160 maybe replaced by a plurality of individual excitation light sources 200integrated into each of the optical modules 15 of the filter wheelassembly as shown in FIG. 7. The use of individual excitation lightsources 200 permits each light source 200 to be optimized for a narrowspectrum range and power profile. As shown in FIG. 8, each opticalcomponent module 15 may comprise a narrow band excitation light source200 in addition to filters, dichroic reflectors and apertures tuned fora specific excitation/emission light frequency combination. Each of thenarrow band excitation light sources 200 may comprise one or more LEDsor lasers, or other suitable light source, and may further compriseselective wavelength filters 210. An associated electrical powerconditioner 220 may provide electrical power, necessary to operate eachof the narrow band excitation light sources 200. The power conditioner220 may perform any or all of the following functions: electricalconnection, rectification, regulation, voltage conversion, AC/DC orDC/AC conversion, or voltage adjustment. Each of the electrical powerconditioners may obtain its primary power from a power source (notshown) located external to the filter wheel. In non-limitingembodiments, primary electrical power may be conveyed from the powersource to the rotating filter wheel 10 by conduction using slip-rings(not-shown), or by inductive coupling using a rotary transformer 230.Alternatively, batteries or other energy storage devices mounted on thefilter wheel may provide primary power for the filter wheel. Each of theelectrical power conditioners 220, mounted on the filter wheel 10,converts the primary power to the electrical power format required bythe corresponding excitation light source 200. In an embodiment, thelight source 200 may be instrumented with sensors 240 for monitoring theperformance and characteristics of the light source 200. The sensoroutputs may be fed back to the electrical power conditioner 220 and usedto adjust the output of each power conditioner 220 thereby maintainingexcitation light characteristics.

Statement Regarding Preferred Embodiments

While the invention has been described with respect to preferredembodiments, those skilled in the art will readily appreciate thatvarious changes and/or modifications can be made to the inventionwithout departing from the spirit or scope of the invention as definedby the appended claims. All documents cited herein are incorporated byreference herein where appropriate for teachings of additional oralternative details, features and/or technical background.

1. A filter wheel apparatus comprising: a planar circular base memberwith a mechanical shaft coupler located at an axis of rotation definedperpendicular to and centered on said circular base member, saidcircular base member penetrated by a plurality of base apertures whosecenters are angularly spaced about the circumference of a circle, saidcenters of each of said base apertures defining an aperture axisperpendicular to plane of said aperture, said planar circular basemember further comprising a corresponding plurality of reflector supportstructures, each of said reflector support structures being located inproximity to each of said plurality of base apertures; a plurality ofdichroic reflectors that transmit light at a first band of wavelengthsand reflect light at a second band of wavelengths, each of saidplurality of dichroic reflectors affixed to one of said reflectorsupport structures and thereby intercepting said aperture axis andoriented at a predetermined angle relative to the plane of said baseaperture.
 2. The filter wheel apparatus, in accordance with claim 1,further comprising: a right circular cylinder member surrounding andattached to said planar circular base member thereby forming acylindrical perpendicular wall; a plurality of wall apertures formed insaid cylindrical perpendicular wall at angular locations correspondingto said plurality of base apertures, each of said wall aperturesdefining a wall aperture axis centered on and perpendicular to said wallaperture and intercepting a corresponding dichroic reflector.
 3. Thefilter wheel apparatus, in accordance with claim 2, wherein said rightcircular cylinder member is formed integrally with said planar circularbase member.
 4. The filter wheel apparatus, in accordance with claim 1,wherein each base aperture comprises an optical filter.
 5. The filterwheel apparatus, in accordance with claim 1, wherein each wall aperturecomprises an optical filter.
 6. The filter wheel apparatus, inaccordance with claim 1, wherein each said reflector support structurefurther comprises an individual excitation light source oriented toradiate toward said dichroic reflector.
 7. The filter wheel apparatus,in accordance with claim 6, wherein said individual excitation lightsource is at least one light emitting diode (LED).
 8. The filter wheelapparatus, in accordance with claim 6, wherein said individualexcitation light source is at least one laser.
 9. The filter wheelapparatus, in accordance with claim 6, wherein said planar circular basemember further comprises at least one electrical power conditioner, saidat least one power conditioner electrically connected to said individualexcitation light source.
 10. The filter wheel apparatus, in accordancewith claim 9, wherein said planar circular base member further comprisesa portion of a rotary transformer, said portion of rotary transformerelectrically connected to said electrical power conditioner.